Styrenic resins can have excellent mold processability, impact strength, and appearance and have accordingly been widely used in the production of many electric or electronic goods. When a rubber modified aromatic vinyl copolymer resin is used in the production of heat-emitting products, the resin should further have flame retardancy.
A halogen-containing compound and an antimony-containing compound can be added to a rubber modified aromatic vinyl copolymer resin to impart good flame-retardant properties to the resin. However, there are health concerns associated with the use of many halogenated compounds such as polybromodiphenyl ether, which is typically used as the halogen-containing flame retardant. Accordingly, a major concern in this field is the development of a flame retardant-rubber modified aromatic vinyl copolymer resin which is prepared without a halogen-containing compound.
Phosphorous, silicon, boron, or nitrogen compounds can be used as halogen-free flame retardants in resin compositions. However, such compounds may not impart sufficient flame retardancy.
Journal of Polymer (Elsevier Science, 1975, vol. 16, pp 615-620) discloses that rubber modified styrene-containing resins have a low Limiting Oxygen Index (LOI), because they do not form char during thermogravimetric analysis (TGA) and combustion. Halogen-containing compounds can readily impart a desired degree of flame-retardancy to a resin, regardless of the kind of resin. On the other hand, as noted herein, rubber modified styrene-containing resins hardly contain char and thus it is difficult to impart sufficient flame retardancy to such resins using only phosphorous- or nitrogen-flame retardants, because these non-halogenated flame retardants typically act on the solid phase.
In order to solve the above problems, U.S. Pat. Nos. 5,061,745, 5,204,394, and 5,674,924 disclose resin compositions that acquire flame retardancy by blending a rubber modified aromatic vinyl copolymer resin, a polycarbonate, and a phosphate ester compound. The presence of the polycarbonate resin makes it easier to impart flame retardancy to the rubber modified aromatic vinyl copolymer resin. However, the composition must include a relatively high amount of polycarbonate (at least 60 parts by weight) to obtain sufficient flame retardancy.
U.S. Pat. Nos. 4,618,633 and 6,716,900 disclose compositions which introduce a polyphenylene ether resin having higher char-forming ability than polycarbonate to a rubber modified styrene copolymer resin. However, it can be difficult to mold the blend of the polyphenylene ether resin and the rubber modified styrene copolymer resin because there is a large difference between the molding temperature of the polyphenylene ether resin and the rubber modified styrene copolymer resin. In general, the polyphenylene ether resin is an engineering plastic molded at a high temperature. In contrast, the rubber modified styrene copolymer resin is molded at a relatively low temperature. Furthermore, the polycarbonate and the polyphenylene ether resin are expensive as compared with other resins, resulting in increased production costs.
The present inventors have developed a resin composition comprising a rubber modified aromatic vinyl copolymer resin, a polycarbonate and a polyethylene terephthalate resin. The polyethylene terephthalate resin has aromatic rings and oxygen atoms in main chain, which tend to form char. However, polyethylene terephthalate resin is a crystalline polymer and polycarbonate is an amorphous polymer. According, blending polyethylene terephthalate resin with polycarbonate resin can deteriorate impact resistance due to phase separation.